(a) Field of the Invention
The present invention relates to a magnetic disk apparatus, more particularly to a magnetic disk drive apparatus having a housing equipped with a spindle for supporting a plurality of magnetic disks. The spindle holding mechanism supports the spindle in rotation and ensures precise alignment of the spindle within the housing.
(b) Related Art Statement
In a conventional magnetic disk apparatus, a spindle for fixedly supporting a plurality of magnetic disks is rotatably held on a base which is part of a housing. Such mechanism for holding a spindle is disclosed in, for example, Japanese Unexamined Patent Publication No. 58-184318. The mechanism for holding a spindle of this type is discussed hereinafter, with reference to FIGS. 1 to 4. FIGS. 1 and 2 are schematic section views showing a main portion of the spindle holding mechanism.
In FIGS. 1 and 2, a plurality of magnetic disks 1 are fixedly supported on a spindle 2, and the spindle 2 is rotatably supported on a base 4 through two bearings 3a and 3b which are disposed at the upward and downward positions of the spindle 2 respectively. The spindle 2 is adapted to be driven by an electric motor 8 composed of a rotor 8a fixed at one end of the spindle 2 and a stator 8b fixed to the base 4.
A holding member 5 is fixed on the periphery of the outer ring of the bearing 3b, and there is provided a compressive spring 6 for depressing the holding member 5 in the axial direction between the holding member 5 and the base 4 as shown in FIG. 1. A compressive spring 7 for pressing the holding member 5 in the radial direction, between the holding member 5 and the base 4, is provided as shown in FIG. 2.
In FIG. 2, as shown by a mark A, a compressive contact member 7a for transmitting the resilient force of the compressive spring 7 is arranged at the periphery of the holding member 5 to effect a surface contact, and the holding member 5 is formed such that a portion of the periphery of the holding member 5 can contact, in a form of substantially line contact, the inner wall of the base 4 as shown by marks B and C. The inner wall of the base 4 is formed in a cylindrical form, and further the periphery of the holding member 5 is formed such that the curvature of the periphery of the holding member 5 at the portion to which the compressive contact member 7a is in contact, is substantially equal to the curvature of the inner wall of the base 4, while the curvature at the periphery portion 5a between the line contact portions B and C is larger than the curvature of the inner wall at the portion opposite to the periphery portion 5a. Thus, the holding member 5 is pressed against the inner wall of the base 4 by the resilient force of the compressive spring 7.
On the other hand, the outer ring of the bearing 3b is depressed in the axial direction through the holding member 5 by the resilient force of the compressive spring 6 in the axial direction. This pressure affects the inner ring of the bearing 3a through the inner ring of the bearing 3b and the spindle 2, whereby both bearings 3a and 3b are affected with a thrust pre-load for relatively shifting the inner ring with respect to the outer ring in the axial direction. By this, both bearings 3a and 3b are mutually prevented from a radial deflection.
Furthermore, the outer ring of the bearing 3b is depressed in the radial direction through the holding member 5 by the resilient force due to the compressive spring 7 in the radial direction, whereby the bearing 3b is depressed against the base 4 thereby maintaining the rotational axis position of the spindle 2 in a constant position.
According to the magnetic disc apparatus equipped with the spindle holding mechanism mentioned above, in the case of thermal expansion being produced in each of the parts by a temperature differential within the housing due to motor head and heat from the high speed rotation of the magnetic disks, there is a possibility of generating a deterioration of precision in mutual position between the magnetic disks 1 and the base 4. To avoid such deterioration of the precision in position, the base 4 and the magnetic disks 1 are made of Aluminum thereby both having the same thermal expansion coefficient.
However, since the bearing 3a out of two bearings for supporting the spindle 2 with respect to the base 4 is fixed to the base 4, a thermal stress is undesirably generated between the base 4 and the outer ring of the bearing 3a on the basis of a difference in thermal expansion coefficient between the materials, i.e., normally steel or the like, composing the bearing 3a and the material, i.e. Aluminum, composing the base 4, thereby generating a deformation or distortion of the base 4 and the bearing 3a. If such deformation of the base 4 and the bearing 3a is generated, as schematically shown in FIGS. 3 and 4, a deviation .DELTA.X, i.e. error, in mutual position is undesirably produced between the magnetic disks 1 and magnetic heads 10 mounted on a carriage 9 moving on the base 4. It is inevitable for the development of the magnetic disk apparatus to restrict the deviation .DELTA.X in the mutual position between the magnetic head 10 and the magnetic disk 1, if possible, on the basis of the thermal stress mentioned above.